Giorgio Serino, Mariacristina Spizzuoco - ReluisActivity 1. Seismic retrofit and improvement of...

G. Manfredi, M. Dolce (eds), The state of Earthquake Engineering Research in Italy: the ReLUIS-DPC 2010-2013 Project, 295-326, doi: 10.14599/r101307, © 2015 Doppiavoce, Napoli, Italy

DEVELOPMENT AND ANALYSIS OF NEW TECHNOLOGIES FOR SEISMIC UPGRADING

Giorgio Serino, Mariacristina Spizzuoco

Dept. of Structures for Engineering and Architecture, Univ. of Napoli Federico II, Napoli, Italy [email protected]

1 INTRODUCTION

Seismic isolation and energy dissipation technologies, although today mature from the scientific point of view and of sure efficacy, require further deepening in the perspective of their possible applications on a large scale in order to reduce seismic risk of constructions in Italy, and of reduction of costs. All these aspects have been confirmed by the experience of the last Italian earthquakes. Particularly with reference to the design of seismic retrofit and improvement interventions on existing structures, it should be important to know when seismic isolation is more convenient in safety and economic perspectives, and which technological solution is more appropriate. As regards energy dissipation systems, to which codes refer in a less clear way, the delivery of guidelines for the design of such systems is necessary, also on the base of the results of the research developed within Line 7 of previous DPC-ReLUIS 2005-2008 project. Furthermore, although semi-active control systems cannot be considered for widespread applications, due to their complexity and to very low probability of events able to activate them during life of construction, they could be more useful in structures equipped with seismic monitoring and/or early warning systems. Italy surely holds an important record in the development and manufacturing of structural bearings for bridges and other civil applications on a worldwide scale. Moreover, our Country is on the cutting of edge in the seismic isolation field exporting rubber-steel isolators all over the world. High costs and weight characterize all steel laminated rubber bearings. Taking into account that the most of seismic area are in developing countries, these aspects cannot be disregarded. The recent realizations triggered the development of new technologies for structural isolators such as friction pendulum systems (FPS) with one, two or three sliding surfaces; in this framework emerged the needs for new design tools and procedures to allow the spreading of base isolation in the common practice. More recently, other research ideas have been developed, as the one of elastomeric bearings in which the elastomer layers are made of recycled rubber and the steel reinforcement is substituted by fiber layers: this innovative bearings are able to reduce both the high cost and weight characterizing the traditional steel-laminated rubber bearings. The effectiveness of a base isolation system (BIS) depends on its filtering capacity over the range of frequencies where seismic energy is larger. However, filtering action of a BIS has, on occasions, to be applied to an unpredictable excitation having random dynamic characteristics: it is known that even when detailed data from previous seismic events are available, the hazard should be derived from more than one seismic source, and it is

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impossible to define a single earthquake scenario that is compatible with the results of probabilistic seismic hazard assessment. Therefore, it is clear that the first natural frequency can never shift out of the “possible” energy content frequency range for any type of seismic excitation. The new idea of a hybrid system, based on a combination of the tuned mass damper strategy and base isolation (TMD + BIS), came from the observation that the response of properly designed isolated systems is dominated by the first-modal contribution and that TMD is able to reduce solely that fundamental vibration mode. The objective is to protect the BIS from those excitation components, which are close to the natural vibration frequency, by controlling the amplitude of the fundamental modal contribution due to the TMD action installed on the base isolation layer.

2 BACKGROUND AND MOTIVATION

Today the base isolation and the energy dissipation strategies lead to very attractive possibilities to favorable control the seismic behavior of structures. However, how it is well known, both these innovative protection strategies could still have difficulties to guarantee the right effectiveness and robustness due to the lack of knowledge of input signals, for the case of base isolation, or due to the lack of design procedure to optimally allocate the damping resources in the case of framed structures, particularly for the case of irregularity. The main motivations of the research of Task 2.3.2 of DPC-ReLUIS 2010-2013 project are: • The need for the implementation of clear and reliable design tools for base isolation

systems applied to new and existing (retrofit) structures (both buildings and bridges). • The still incomplete knowledge about ultimate limit states of the High Damping Rubber

Bearing (HDRB) devices for base isolation: design codes only give general design criteria, not accounting for all possible failure modes and local effects that affect the collapse.

• The need to detect the perspectives and the limits of the new technologies, such as FPS devices, that, despite the great number of experimental tests performed, have not yet been tested during a real earthquake, i.e. there are still unknowns about their behavior in limit conditions (collapse, uplift, excessive heating of sliding surfaces, etc.).

• The necessity to study the properties of self-lubricating materials for the sliding surfaces: large values of friction provide high damping capacity, but also high lateral stiffness, and promote a huge increase in temperature at the sliding interface, which in turn affects the properties of the friction materials.

• The idea of reducing both the high cost and weight characterizing the traditional steel-laminated rubber bearings, by developing new elastomeric bearings in which the elastomer layers are made of recycled rubber and the steel reinforcement is substituted by fiber layers.

• The necessity of harmonizing the different procedures aimed at the design of seismic control systems based on the use of passive devices, in order to define simple and shared design criteria that can be suggested to professionals when approaching to such kind of technologies.

• The consideration that semi-active control systems, at the current state of knowledge, involve a relatively high complexity in their implementation and management: although this complexity seems to represent today a strong limitation to the practical use of such technology for civil construction, these systems may however be of interest for structures already equipped with seismic monitoring and/or early warning systems.

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3 RESEARCH STRUCTURE

The main objectives of the research within Task 2.3.2 consist of outlining: 1) The study of the response of seismically isolated buildings featuring an inelastic

behaviour of the superstructure, in order to assess the applicability and effectiveness of seismic isolation for the seismic improvement of existing buildings.

2) The evaluation of the effectiveness of devices for the protection of existing buildings and precast systems, from both structural and economic points of view.

3) The definition of suitable techniques for the insertion of devices on existing buildings and precast systems.

4) The study of robustness and effectiveness of the combined strategy TMD + BIS. 5) The delivery of design technical indications to retrofit or to improve the behaviour of

existing non-ductile reinforced concrete (RC) buildings by means of dissipative systems such as buckling restrained braces and HDR-based devices: preliminary design criteria, reliability of simplified analysis methods (behaviour factors, equivalent damping) and feasibility problems (detailing and interaction with non-structural elements, positioning within the existing structure).

6) The development of simplified formulas (in terms of reduction factors for the earthquake forces) for the seismic design of structures which exploit the combined effects of viscous and hysteretic dissipation, as provided by dampers and by post-yielding behaviour of the structural members, respectively.

7) The creation of a database of properties of current sliding materials and the delineation of the relationship between their friction and physical/mechanical properties.

8) The development and characterization of novel frictional materials with optimal properties for use in seismic isolation systems.

9) The theoretical and experimental study of the combined use of three different technologies, having some shared aspects and tools involved: the semi-active control, the structural monitoring, and the seismic early warning. The aim is the accurate identification of sensors and electronics needed for semi-active control, monitoring and seismic early warning systems, the investigation on the possible use of components shared by two or all the above systems. A laboratory testing campaign will be designed in order to experimentally highlight the feasibility and effectiveness of the proposed solutions, also with a view for optimizing performance and costs, and to measure these benefits in terms of robustness with respect to the protection that can be offered by purely passive systems.

In order to better organize the work considering the different activities and objectives of the research, Task 2.3.2 has been organized in four Activities, and two coordinators have been nominated for each Activity (Activity 3 has been included in Activity 1 after the discussion). The organization of the Task in Activities allows to significantly improve the coordination among Research Units on specific topics and to more efficaciously develop joint experimental activities. Activity 1. Seismic retrofit and improvement of existing buildings through seismic isolation (includes bridge piers with seismic isolation). The activity plans the study of standardized operational methodologies for the insertion of devices at the base of existing buildings paying a special attention to masonry buildings. It also concerns the pointing out of the recurrent work typologies for inserting devices. For these typologies, the operational successions are being developed with a particular focus on the constructive aspects of each phase: access to the sub-structure, preliminary works, strengthening of the sub-structure, performing the super-structure detachment, creating the


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spaces for the devices, installation of devices, successive works, final solution of continuity, collateral problematics. The activity also includes the development of simplified methodologies for defining the optimum isolation thresholds, as a function of the usable devices and of the collapse mechanisms of the super-structure. Evaluations of the economic compatibility of the seismic improvement through isolation are also carried out. Activity 2. Development of new isolating devices, also low-cost. The activity includes the study of cost-effective devices that can be inserted within the connection joints of the precast constructive systems: economic, constructive as well as performance aspects are being considered at the same time. The protection systems can be based on friction devices, sliding devices, plastic devices, and other dissipating devices. Their concept and assembly should be simple for containing the costs, for avoiding constructive complications, for allowing adaptation to the pre-existent productive lines, for being characterized by an economic compatibility of the whole project. The goals of the application of protection systems to the precast systems are: the increase of the seismic capacity of the earthquake-resistant system, to make compatible the use of non-optimal construction systems in earthquake prone areas, and the reduction of the construction cost of the elements for compensating the cost of the devices. For all the proposed innovative devices, the program of the activity consists on the definition of the geometry and the best materials to develop the isolators, the planning of the testing activity on prototypes, the theoretical study of defined prototypes, and the experimental activity on prototypes. The activity is also focused on testing and characterization of the sliding properties of current self-lubricating materials, development of a database of properties and formulation of “structure – property” models, development of frictional materials with optimal friction coefficient and improved load bearing capacity and wear endurance, performance of dynamic tests on real scale isolation systems employing the novel frictional materials. Activity 3. Manual with guidelines for the design of passive energy dissipation systems. This activity consists in: selecting some simplified method, among those available in technical literature and/or developed by the Research Units, for the preliminary design of structures retrofitted by elastoplastic and viscoelastic dampers; evaluating the effectiveness of the simplified design method by using a probabilistic methodology accounting for the uncertainties of the earthquake action and of properties of the bare and retrofitted structures; in selecting case studies to develop benchmark applications, and in developing optimal constructive details for the benchmark applications. An applicative manual represents the product of the activity. The aim of the applicative manual is to guide the professional engineer from the choice of a target reduction in the seismic response of the structural system (with respect to the response of a structure without any additional damping devices), to the identification of the corresponding damping ratio and the mechanical characteristics of the commercially available dampers to be inserted in the building. Besides, the coupling of viscous and hysteretic dissipation will be investigated. The central issue behind this idea lies in the determination of the correlation between the force reduction factor and the ductility demand, when viscous dampers are located inside the structure. Such correlation has broadly been studied in the past for structures not equipped with additional dampers, and represents the heart of the usual seismic design methodologies. According to the framework of the conventional design procedure (response spectrum analysis with force reduction factor), the purpose of the research work is to provide a proper value of the force reduction factor for structures characterized by high level of damping (e.g. damping ratio


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equal to 30%). This value should allow to reach the same safety level actually provided by the code for the same structure without dampers. In more detail, the relationship between the force reduction factor and the ductility demand will be investigated in order to understand how it is influenced (i) by the presence of additional viscous dampers and (ii) by high values of damping ratio. Activity 4. Integration among semi-active control, monitoring and early warning systems. In the framework of “seismic isolation of bridges”, this activity consists in investigating the addition of semi-active devices to a seismic isolated bridge, and then defining a standard method to evaluate the amount of supplemental damping given by variable dampers installed between piles and deck of isolated bridges. As regards to the “semi-active control combined with monitoring and EW”, the activity is focused on the: 1) Analysis of sensors and electronics needed for: - Semi-active control activity: elements of input (sensors and conditioners), processing

elements (hardware and software), control elements (devices, electricity and power), laboratory and on-site systems (operational possibilities and comparison).

- Monitoring: elements of input (sensors and conditioners), processing elements (hardware and software), laboratory and on-site systems: (operational possibilities and comparison).

- Seismic Early Warning: elements of input (sensors and conditioners), processing elements (hardware and software), laboratory and on-site systems (operational possibilities and comparison).

- Combined use of the three technologies: common elements and needed integrations. 2) Experimental activity (JET-PACS model derived from the previous ReLUIS Project): - Semi-active control: designing the tests referring to the number and positioning of the

devices, selecting the control algorithms, discussing the level of dissipation/force amount to be given.

- Semi-active control combined with monitoring and seismic EW: designing the tests considering different algorithms (corresponding to a smart passive or semi-active use of the variable devices), discussing the level of dissipation/force amount to be given.

- Comparison in terms of costs and structural performance in respect to passive systems.

4 MAIN RESULTS

4.1 ACTIVITY 1: Seismic retrofit and improvement of existing buildings through seismic isolation (includes bridge piers with seismic isolation)

4.1.1. Operational aspects regarding the installation of isolators at the base of existing masonry buildings (case studies) and estimation of costs The following activities were performed: • Completion of the classification of the critical aspects concerning the insertion and location

of isolating devices below existing masonry buildings have been pointed out and the solution strategies have been outlined.

• Completing the outlining of the procedures, technologies and operational modalities for the cutting of existing masonry.

• Completion of the definition of the operational phases and the related works for placing the devices below masonry buildings.

• Completion of the outlining of solutions for maintaining the compatibility of the existing vertical communication systems within the isolated configuration.


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• Arrangements of local/partial seismic isolation on historical buildings have been drawn to eliminate the vulnerability of particularly critical structural macro-elements.

• Suitable procedures of Performance Based Seismic Design (PBSD) for the evaluation of the economic compatibility of the base-isolated option for the seismic protection of an existing building have been outlined and applied to real study cases.

• The procedures, technologies and solutions outlined for the insertion of base isolation within existing masonry structures are being critically verified through the application to the design and the building of real study cases.

• Real applications of seismic isolation have been developed even on historical buildings within the ambit of cooperation projects established with structural designers.

4.1.2. Evaluation of the inelastic behaviour of existing RC frame structures retrofitted through base isolation The parametric study on the inelastic behaviour of RC frame buildings with seismic isolation has been further developed by focusing the attention on the seismic effects of infilled masonry panels. Furthermore, the research has been focused on the application of seismic isolation for the seismic rehabilitation of a real RC frame building, accepting limited plastic deformations in the superstructure under strong earthquakes. This situation is representative of what would happen if seismic isolation was designed considering, for existing buildings, seismic rehabilitation objectives somehow inferior to those typically adopted for new buildings but still superior to the basic safety objectives that must be achieved in any rehabilitation project. The achievement of the target objectives of the design has been verified through nonlinear dynamic analyses. The selected case study is represented by a 4-storey building with a rectangular plan of approximately 230 m2, characterized by internal frames in only one direction and no openings in the infills of the weak direction. In the numerical model for nonlinear dynamic analyses, the plastic hinges of beams and columns have been modeled using link elements characterized by an hysteretic degrading cyclic behaviour (Takeda degrading-stiffness model). The shear strength of the structural members has been suitably taken into account in the numerical model. Finally, the infilled masonry panels have been modeled as equivalent struts, considering an elastic-fragile cyclic behaviour. Three different types of isolation system have been alternatively considered, i.e.: (i) HDRB, (ii) HDRB + flat surface sliding bearings, and (iii) curved surface sliding bearings (FPS). The nonlinear dynamic analyses of the selected case study are aimed at investigating also a series of critical aspects relevant to the application of seismic isolation for the rehabilitation of existing RC frame buildings, i.e.: (i) influence of the variability of the mechanical behavior of the isolation devices (variability of the friction coefficient for FPS, effects related to scragging, temperature and axial load for HDRB, etc.); (ii) differences related to the modeling technique (linear equivalent or non-linear) adopted for the isolation system; (iii) effects due to the use of commercial isolation devices instead of "ad hoc" isolation devices. The results obtained so far, considering HDRB and HDRB + flat surface sliding bearings at standard temperature (20 °C), indicate that the global ductility demand to the superstructure is substantially in line with those obtained examining the 2-DOF models. The analyses conducted on the 3D model also permit to obtain detailed information on the local behaviour of the structure. In particular, the results of the analyses, for instance, show that values of global ductility demand of 2 are associated to plastic hinges rotations of beams and columns between the limit values corresponding to Immediate Occupancy (IO) and Life Safety (LS) Performance Levels, according to FEMA356. However, the results also indicate the critical role of the short columns intercepted by the knee beams of the stairs, which undergo plastic


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hinge rotations higher than the limit values corresponding to Life Safety Limit State, thus requiring local strengthening. The analyses have also pointed out the influence of the solutions "from catalog", for what concerns the choice of the isolation devices, on the design objectives of the seismic rehabilitation, with respect to “ad hoc” solutions optimized for the purpose. A numerical study was carried out, aimed at evaluating the applicability and effectiveness of seismic isolation for the rehabilitation of RC frame buildings. The aforesaid study is based on nonlinear time-history (NTH) analyses carried out using 3D models. A set of 7 natural accelerograms has been selected using the software REXEL-DISP. These signals are spectrum-compatible with the target spectrum for L'Aquila (soil B and topographic category T1). Four multi-storey RC frame buildings, designed for gravity loads only, have been selected as building prototypes. The buildings feature a substantially symmetric structural layout in both horizontal directions, floor area of approximately 230 m2 and number of storeys ranging from 2 to 8. Three different types of isolation systems (IS) have been examined: HDRB, HDRB+flat sliding bearings and FPS. The methodology of the research activity has been developed in two phases. First of all, the IS has been designed to provide an elastic behavior of the superstructure (SS) in case of severe motions. In this case, devices displacements of approximately 50 cm have been found. These values are certainly incompatible with the maximum displacements guaranteed by the seismic devices currently in use. In the second phase, using a simplified procedure based on a 2D model developed during the first year of the research project, the IS has been re-designed so as to contain the extent of the displacements while accepting the plasticization of the SS. The NTH analyses carried out during this phase showed (for each IS type) a significant reduction of the IS displacements as well as a substantial compatibility between 3D and 2D models in terms of ductility demand to the SS. In the 3D model, the structural behavior at the local level has been evaluated in terms of plastic hinges rotation of beams and columns considering also the brittle mechanisms due to shear stresses. The inelastic response of the structure, evaluated as described above, is consistent with the expected performances. The verifications in terms of shear indicate the critical role of the short columns intercepted by the knee beams of the stairs. Basing on the results obtained during the third year, guidelines are proposed. The main points are summarized below: (i) the collapse limit state of seismically isolated structures should be based on the lateral capacity of the SS without significant reliance on its inherent hysteretic damping or ductility capacity; (ii) particular attention shall be paid in the selection of an acceptable value of the global ductility demand to the SS, in particular, the choice must be carried out considering the structural characteristics of the building and more importantly its inelastic mechanism, i.e.: μd=2 (q≈2.5) for buildings featuring a weak-beam/strong-column inelastic mechanism, being associated to plastic hinge rotations in beams (and columns) between the limit values corresponding to SLD and SLV, μd=1.5 (q≈1.5-2) for buildings featuring a soft-storey mechanism, being associated to plastic hinge rotations in columns consistent with the limit values corresponding to SLD; (iii) brittle failure should be avoided. 4.1.3. Theoretical study of the dynamic behaviour of isolated structures in phase space / Seismic response analysis of structures with pendulum isolators under near-fault events The research group has continued research on innovative strategies for seismic protection which use isolation and energy dissipation. At the time, the attention is mainly faithful to the study of innovative design procedure to achieve robust and/or optimal strategy to control the


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seismic behavior of framed structures. In the following the main results for base isolation strategy are represented. The seismic behaviour of base isolated buildings has been analyzed by using an innovative mathematical formulation in the state space, that allows us to describe the dynamic response of structures in the case of non-classical damping. Particularly, the seismic response of base isolation with linear–viscous behaviour is herein investigated by studying the mode shapes, the frequencies and the modal participation factors, that are obtained by the proposed formulation varying the main design parameters. In such a manner, the effect of these parameters on the isolated structure behaviour as a whole is evident. As examples, the following Figures 1 and 2 show the frequencies and the modules of the modal participation factors associated with the first and the second mode shapes of the isolation devices.

Figure 1. Frequencies associated with the first and second modal shapes evaluated for γ=0.1.

Figure 2. Modules of the modal participation factors associated with the two modal shapes

evaluated for γ=0.1. The obtained results lead to the following main conclusions: • values of the damping factor of isolation devices higher than 0.35 cause a worsening of

the superstructure response; • low values of the mass ratio, less than 0.2, can lead to a worst behaviour of the

superstructure. Moreover, high values of the degree of coupling can lead to an inversion of the mode shapes;

• values of degree of coupling near to 0.5 lead to inside resonance effects between base isolation and superstructure which maximize the effective damping on the first mode shape;

• high values of the mass ratio, greater than 0.9, can lead to overdamped behaviour in the second mode shape for greater values of the isolation factor damping and the degree of coupling. In particular, values of greater than 0.30 lead to a worst behaviour of the superstructure.

For the case of Friction Pendulum Bearings (FPB) the research aims to investigate cases where the vertical component of seismic motion is relevant like that of nearfault events. To investigate the potential performance that could be achieved by FPBs, the study considers an ideal isolated system characterized by a perfect rigid superstructure neglecting lateral-torsional effects. In particular, a nonlinear 3-DOF system has been described in SAP2000 to analyze the seismic response to recorded nearfault events like L’Aquila 2009 and Emilia Romagna 2012. The analysis of results shows that the vertical component of seismic events could significantly affect the behavior of the isolated structures in the case of FPBs.


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4.1.4. JETBIS Project: set up of experimental physical model (one-story steel building, isolated at the base by different isolation devices analyzed within the Task), definition of experimental tests program on shaking table and characterization test of devices All the steel elements (plates, special components, etc.) needed to complete the experimental set-up of the shaking table tests campaign on the base isolated structure (Figure 3 and 4), were designed and prepared. The Research Unit of Naples Federico II, responsible of the shaking table, has developed the configuration of sensors to measure all the required experimental quantities, has defined the seismic inputs, and the type of tests to be performed, in agreement with the other RUs. Shaking table experimental tests were performed on the isolated structure by means of low cost recycled rubber isolator reinforced with layers of high strength quadri-directional carbon fiber fabric (Figure 3, 4 and 5): - dynamic characterization tests of the structure, to the aim of evaluating the first two

frequencies and the corresponding damping factors; - seismic tests through the application of seven properly selected natural earthquakes; - fatigue tests by the application of a moderate earthquake to the base of the structure, for

twenty times, to the aim of verifying the degradation of the isolators.

Figure 3. Experimental base isolated structure.


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(b)

Figure 4. Experimental frame structure and additional base horizontal frame.

Figure 5. Low cost isolator mounted under the isolated structure. Shaking table testing was carried out on 1/3 scaled structural steel model protected seismically using Double Concave Friction Pendulum base isolators (DCFP). These isolators were produced by FIP-Industriale (FIP-D isolator – Figure 6). Testing demonstrated the effectiveness of the isolation system across the various testing configurations (model with masses both symmetrical and eccentric, isolators with and without lubrication). Before shaking table testing some characterization test on DCFP was carried out at Seismic Laboratory of the University of Basilicata. The bearings were tested under a N = 32 kN design vertical compressive load. A series of sinusoidal lateral displacement histories has been imposed in accordance with testing of Curved Surface Sliders prescribed by Eurocode (UNI-EN 15129, 2009). Figure 7 shows experimental force-displacement relationships of the devices carried out on different conditions of surfaces: i) Standard, ii) Lubricated (SL) and iii)


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Not-lubricated (SNL). A silicone based (lithium soap) lubricant was applied to the top and bottom face (μ1 = μ2) of the rigid slider. Figure 7 shows also the numerical simulations results obtained by considering both constant and variable friction models.

a) b) c) Figure 6. a) functioning scheme of the DCFP device; b) overview of the DCFP device; c) theoretical

hysteresis cycle of DCFP bearing having equal radii of curvature and equal friction coefficients.

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Figure 7. Experimental and numerical Force–displacement at peak velocities of 50 and 400 mm/s. Both

tests were conducted on Standard, Lubricated (SL) and Non-lubricated (SNL) surfaces. The shaking table tests demonstrated also the potential for the use of low-cost and low-quality elastomers for the production of fiber reinforced bearings. Low-performance materials are suitable because the bearings are unbonded and reinforced with flexible fiber sheets. In this configuration, devices can deform freely without generating high tensile stress, which is common in transversal layers of conventional isolators. The absence of tensile stresses prevents the vulcanization of rubber to the reinforcements. For instance, devices for the tests were manufactured by gluing layers of a recycled elastomer to layers of fiber reinforcements with a polyurethane adhesive, without the need for costly and

Characterization TestConstant friction modelVariable friction model


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high-energy demanding vulcanization processes. The proposed devices are low-cost and eco-friendly. A series of 27 records was employed for the shaking table experiments. The selected ground motions were representative of moderate to high seismic regions in Italy. With such severe inputs, the bearings performed exceptionally well. They demonstrated robust behavior and re-centering capabilities in all tests; a visual inspection of the devices confirmed no damage. The tests gave a preliminary assessment of the viability of the concept. Future multi-directional experiments are required for a complete understanding of the nonlinear behavior of the proposed base isolation system and for its acceptance by the construction industry. The proposed technology could influence the retrofitting of historic buildings and unsafe public housing in seismic-prone regions of the world. 4.1.5. Observatory of Isolated structures in L’Aquila / Artificial “isolated” soil The following activities were performed: 1. institution observatory on isolated structures built in l’Aquila; 2. seismic analysis of an artificial "isolated" ground. Regarding the observatory on isolated structures in L'Aquila (point 1), data on isolated buildings were collected, build, in stages of construction or planning in the area of L'Aquila, in order to create a database (n. of elastomeric isolators and FPS, design displacement; period of isolation; maximum vertical load, etc.) useful for the design and control of seismic isolated buildings. Concerning the artificial "isolated" ground (point 2), 2 seismic isolated plates of more than 26000 m2, with overlying buildings with a number of storeys between 1 and 15 (Figure. 8), had been designed and analyzed. The isolation of the artificial ground and of all the above buildings was achieved by placing the plates on elastomeric isolators arranged head to the columns of the basement (parking). The performed numerical analyses showed that the ''isolated'' artificial ground can decouple the vibration modes of the structural system, despite the overall complexity of the analyzed structural system.

Figure 8. Finite element model of an artificial “isolated” ground with overlying buildings of 1 to 15

storeys.


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4.2 ACTIVITY 2: Development of new isolation devices, also low-cost 4.2.1. Manufacturing of prototypes and execution of experimental tests on new low-cost isolation and dissipation systems The low cost devices proposed are unbounded isolators made of a recycled rubber compound reinforced with carbon FRP layers. The geometrical and mechanical characteristics of the prototype isolators were designed by considering their strength and stability behaviour under the experimental structure. Their experimental behaviour has been studied in detail, by means of compression tests (at the laboratory of the Department of Structural Engineering of University of Naples Federico II – Figure 9), and shear tests (at the laboratory of the Department of Mechanical Engineering for Energetics of University of Naples Federico II – Figure 10). After the experimental tests, the vertical stiffness and the horizontal stiffness have been computed, as well as their variability, respectively, with the vertical loading and applied horizontal displacement. The low cost devices are unbounded isolators made of a recycled rubber compound called “polverino” (10% granules of SBR and 90% very small granules of SBR) reinforced with carbon FRP layers. The geometrical and mechanical characteristics of the prototype isolators have been designed by considering their strength and stability behaviour under the experimental structure.

Figure 9. Shear tests on a prototype recycled rubber isolator.

Figure 10. Compression tests on prototype recycled rubber isolators.


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Dynamic testing have been performed at the structural laboratory of the University of Basilicata, on a 3-storey, 2/3 scaled post-tensioned timber structure (Figure. 11) in order to verify the effectiveness of an innovative protecting system based on the coupling of post-tensioning rods and L-shaped steel dissipating plate elements. The first element provides elastic recentering to the structure when subjected to horizontal seismic excitation while the second one provides additional strength and dissipative capacity. Testing have been performed both with and without the addition of dissipative steel angles.

Figure 11. a) 2/3 Scale Post-Tensioned Glulam Test Frame; b) Post-Tensioned Glulam Frame Beam-

Column Connection; c) Yielding Steel Angle dissipation devices. 4.2.2. Analytical forecast of the mechanical properties of Wire Rope devices, on the base of coils and wires’ geometry The wire-rope devices proposed by the research Unit Naples Federico II have been used for a long time for isolation from vibrations and protection from the bumping of equipment in the military, electronic and air space fields: they consist of cables in stainless steel wound in the shape of a coil or an arc on drilled bars in aluminum alloy; each cable consists of several plaited strands, while each strand in turn consists of several wires, the number of which varies according to the device in question. A peculiar characteristic of the wire-rope isolators is that of being deformable in both the two horizontal and in the vertical directions, and of possessing at the same time a significant dissipation capacity due to the hysteretic damping achieved thanks to the friction produced by the rubbing of the individual strand wires and between one strand and another. The possibility of incorporating the filtering with the dissipative function in a single element makes these devices particularly interesting also for seismic isolation, and suitable in particular for the protection of light but costly equipment, in view of their quite considerable deformability in the vertical direction An analytical study on wire-rope devices was completed (Figure 12), in order to single out the mathematical relationships existing between the geometrical characteristics and the mechanical properties of these kind of devices: this may allow an effective help in the design of the dimensions of wire-rope devices to be manufactured for the isolation of the simple experimental structure.


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(a) (b) (c)Figure 12. (a) Sketch of cable section; (b) loading directions of a wire-rope; (c) drawing of a wire-rope.

4.2.3. Study of mechanical behavior of laminated rubber bearings

The numerical study has been made by developing nonlinear models of equivalent beam for the analysis of buckling (and post-buckling) of fiber reinforced elastomeric isolators (SLFREI), subject to nonuniform shear warping (out of the plane displacements). The models are developed locally in terms of the classical linear analysis and subsequently set coherently in a nonlinear terms within the framework of the implicit corotational method using a quadratic asymptotic development of Biot deformation tensor. With reference to the stability analysis, the results obtained for several different models have been compared with those produced by equivalent beam models established in the literature. The possible failure modes of circular elastomeric isolators (debonding; instability, yielding of reinforcing steel plates; cavitation of the rubber; roll out) have been identified and studied. Then, the domain of stability in Figure. 13 has been defined; it provides the limit medium pressure (Pm) which can be applied to the isolator in the presence of earthquake at different shear distortion (gs). In Figure. 13, Pm,0 is the maximum pressure that can be applied to the isolator for gs=0; S2 is the secondary shape factor. In particular, from the figure it is observed that the domain is delimited at the top by the straight line of Eq. Pm/Pm,0=1-1.2·gs/S2, that is representative of collapse by stability or plasticity of the plates, the lower the curve of Eq. Pm/Pm,0=gs/S2·(G·H/te)/(1-gs/S2), that is representative of collapse for roll out, and on the right from the vertical line of Eq. gs/S2=2/S2 that corresponds to the limitation gs≤200%.

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Figure. 13. Stability domain for circular HDRB devices for base isolation

Compression/Tension

Shear

Roll


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4.2.4. Characterization and design of Rubber-Layer Rolling-Bearing (RLRB) In the first year of research the theoretical model of RLRB has been planned in order to define the fundamental parameters. Activities of the second year have allowed to improve the numerical study of the device, its mechanical design and of its components, studying, also, interaction between steel and rubber in order to understand the consequent behavior of the device. Moreover, it has been developed the plan of the device used in last year of activity to make characterization tests. In the third year of activity, after a prior examination of the device’s peculiarities and links necessary to assembling the device on the test machine, characterization tests have been performed in order to check the operating principle of the device. It has been used an Instron 5869 electromechanical testing machine, with low frequency. Usually, Instron 5869 material-testing machines permits to test the tensile or compressive strengths of a sample material. In this case, by an accurate design of the link components rolling tests have been performed obtaining the hysteresis cycles. Tests have been made changing the normal load on the device by using UPN steel elements used in order to distribute the load in a homogeneous way. The link between steel layers and the tests machine has been studied with a mechanical constrain which permits rotation around a Φ 24 steel shaft and, for the central steel layer, it has been chosen a constrain with a two link point. Characterization tests have been made with 0.05 Hz frequency and realizing five cycles; it has been defined a displacement on the internal plate of +/-25.0 mm. Three different hypotheses about the normal load on the device have been assumed. The first load has been defined in relation to the shaking-table structure, 2.0 tons, and after other two loads of 1 ton and 3 tons have been used to check the behavior of the device. The characterization tests demonstrated the correct behavior of the device in a geometric and dimensional aspect and in performance aspect. The hysteresis cycle, in fact, has been useful to demonstrate the dissipation efficiency of the isolation system, because also the rubber layer has not presented damages because of the high load. Characterization tests, therefore, have not highlighted an unexpected behavior of the device; on the other hand they demonstrated, although in a preliminary way, the efficiency of the RLRB device.

Figure 14. Render of the isolator Rubber-Layer Rolling-Bearing (RLRB).


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Figure 15. Characterization test on RLRB device Figure 16. Characterization test on RLRB device with load 1 ton. with load 2 ton.

Figure 17. Characterization test on RLRB device with load 3 ton. 4.2.5. Development and experimental characterization of a new auto-lubricant material based on optimized PTFE for sliding isolators The following activities were performed: (1) Implementation of three-dimensional finite element models of sliding isolators. (2) Assessment of the thermal-mechanical behavior of sliding isolators in numerical

analyses; investigation of frictional heating and its effect on the dynamic response of the isolators under different loading histories.

(3) Design and production of sliding isolators for tests on shaking table (JetBis project).

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Figure 18. Dependence of the coefficient of friction of metal filled PTFE on sliding velocity (left) and on temperature and accumulated sliding path (right).


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Figure 21. Dynamic properties of the isolation unit (lateral stiffness Keff and Energy Dissipated per Cycle EDC) in shaking tests at different speeds: numerical calculations (FEM) and experimental validation

(EXP)

Figure 22. Temperature distribution of the surface of the friction pad predicted in analyses of

unidirectional tests at different velocities.

Figure 19. Three-dimensional model of the curved surface sliding isolator.

Figure 20. Temperature profiles through the thickness at different points on the surface of

the friction pad.

test velocity [mm/s] Tmax [°C]

Tavg [°C]

D1 85 106 60 D2 170 169 80 D3 340 221 130


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Figure 23. Influence of the loading path (uniaxial vs. biaxial orbits) on temperature distribution on the

surface of the friction pad.

4.3 ACTIVITY 3: Manual with guidelines for the design of passive energy dissipation systems

4.3.1. Definition of design methodologies of dissipative braces for the retrofit of existing buildings With reference to the viscous or viscoelastic dampers (Hwang et al. 2008), the possibility of achieving the seismic protection through the integration of the elastic lateral stiffness resources and the viscoelastic properties of a dissipative bracing-damper system has been investigated. The innovative aspect consists of considering the viscoelastic damping resources as a design variable in order to control the dynamic response. It has been thus proposed and developed an integrated design methodology to ensure a preassigned performance, within the displacement based design approach, which explicitly takes into account the dynamic behavior both of the structural and control systems (Ou et al. 2007). The optimal design criterion has been defined by determining the combination of the variables which minimizes a total cost function evaluated by considering the relative cost between the elastic resources and viscoelastic dissipative ones (Ang and Lee 2001). Then a validation of the integrated procedure has been performed by verifying that the dynamic response of an optimal single-degree-of-freedom integrated system achieves in average the expected performance displacement by considering a set of seven unscaled acceleration records compatible in average with the elastic spectrum relative to the life safety state, provided by the new Italian seismic code. A new strategy of extra-structural dissipation of energy has been studied by taking advantage of the innovative formulation in state space, which allows to describe the dynamic behavior of structures in the case of non-classical damping. The new base damping strategy view the concentration of the dissipation of energy in special devices located at the base of mixed wall systems in such way preserving the structural elements of the superstructure from damage. The research has mainly focused on the development of the guide lines for the design of energy dissipation systems, with particular attention to case studies. Secondly, in order to furnish the design indications, some investigations about the behavior of existing continuous bridges protected by seismic isolators are also carried out. With reference to the first activity, during the second year, a probabilistic methodology that permits to evaluate the seismic vulnerability of the structural systems and the effectiveness of the retrofit based on the introduction of dissipative braces is developed. The methodology is based on the use of local engineering demand parameters (EDPs) for monitoring the seismic response and on the development of component and system fragility curves before and after the retrofit. During the third year the methodology has been extended for the seismic risk assessment, by convolution of the fragility curves built using local and global EDPs with hazard curves corresponding to various hazard scenarios. The methodology has been applied to a benchmark 2-dimensional RC frame retrofitted by introducing Buckling Restrained Braces (BRBs)


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designed for different levels of base shear capacity. according to a design method already validated in the first year of the research. The obtained results have confirmed the efficiency of the retrofit and have shown that, in general, the use of global rather than local EDPs results in lower safety margins. The last period of the third year has been dedicated to develop a benchmark application to introduce into the guide lines for the design of energy dissipation systems. To this purpose several study cases have been analyzed and, at the end, a real RC building composed by 6 levels and built in 1983 (Figure. 24a) was chosen.

Figure 24. Representation of the chosen case study (a) and configuration of dissipative braces (b).

A 3D non-linear model of the frame has been produced by the code SAP 2000 in order to perform a PushOver analysis for evaluating the seismic vulnerability. The results have shown that in both the horizontal directions the obtained frame capacity is significantly lower that the demand. Both elasto-plastic and visco-elastic dissipative braces are considered for the retrofit. To define the characteristics of the dissipative braces the design method validated during the first and second year of the research is used. Different configurations have been developed (Figure. 24b) in order to find the optimal solution. With reference to the chosse solution both the braces components (devices and link braces) have been dimensioned and constructive details have been developed. With reference to the second activity the dynamic properties and the seismic behaviour of isolated bridges with transverse constrains at the abutments has been investigated and simplified procedures for the preliminary design have been developed.

5.35 4.9


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Part of activities 3 were coordinated with the specific task of structural health monitoring. For it have been studied and compared techniques and procedures relating to the parametric identification of structural models representative of frame structures (Antonacci et al., 2012c) . The research group continued the study of the development of possible strategies for structural health monitoring using smart sensors connected to each other through wireless networks (Braga et al., 2012). In this regard it should be noted the improvement of the structural health monitoring for the Basilica of Collemaggio through the installation of 11 exstensometer and 3 inclinometers (Figure. 25). This system, can be useful for a better understanding of the structural behavior, moreover this constitutes a case of study for testing the effectiveness of this new technology (Braga et al., 2012; Braga et al., 2013). Furthermore the RU has continued its studies for the assessment of seismic vulnerability of buildings damaged by the earthquake Aquilano (Cardone et al., 2012; Castaldo et al., 2013), which can provide useful information about the real situations and highlight the possibilities of applications of the technologies studied in this task.

MONITORAGGIO STRUTTURALE DELLA BASILICA DI COLLEMAGGIO Posizionamento sensori multifunzione wireless

Presidenza del Consiglio dei MinistriDIPARTIMENTO DELLA PROTEZIONE CIVILE

Commissario delegato per la Gestione dell’emergenza della regione Abruzzo

CEntro di Ricerca e Formazione in Ingegneria Sismica

Università degli Studi dell’Aquila

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Pianta della Basilica di Collemaggio

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Accelerometro in elevazione

Accelerometro a terra Estensimetro

Inclinometro Nodo Gateway

Figure. 25. Monitoring of the Basilica of Collemaggio: multifunction sensors placement.

4.3.2. Study and delivering of simplified design procedures of dissipation systems based on linear analyses with structure factor The parametric study on the inelastic behaviour of existing RC frame buildings retrofitted with energy dissipation bracing systems was concluded by focusing the attention on the seismic effects on both direction (acting simultaneously) and on medium rise buildings. In line with the studies conducted during previous years, 20 cases of study considering buildings designed for gravity load only, have considered in the parametric analysis. The beam and column dimensions and detailing were keep as typical of Italian construction of the 70’s and 80’s.


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The design of the bracing systems was optimized and applied for each of the 20 basic structures considering both main directions (direction X and Y) and two diverse bracing arrangements (V inverted (V) and diagonal (X)). In each case the same design procedure did not consider any specific intervention to the structural elements (beam and columns) where the bracing was applied. Coherently to previous years, different design targets were used considering (i) 4 values of structural ductility (μ* 1.0, 1.15, 1.3, 1.5) and (ii) 3 values of ductility of the equivalent bracing (μDB 4, 8, 12), a total of 960 cases simulated. The analysis have confirmed the effectiveness of the analytical formula proposed for the calculation of the structural factor for braced buildings qB uses a coefficient C to augment building initial value of q (qC = C *·q). The increase of the structural factor is ranging from 1 to 4 depending on the combinations of design parameters. The best correlation between the values of C evaluated using NLSA and that calculated Ccal considering different combinations of the proposed independent variables was obtained through a linear regression considering only three parameters with higher weight: i) structural ductility μ*; ii) the ratio between the bilinear equivalent period of the braced structure and that of the original structure TB* / T* ; iii) the ratio between the yield point of the bracing and the resistance of the original structure FDB / Fy*. From the analyses performed in order to avoid the overloading of the elements of the original structure it is recommended that: i) the yield force of the equivalent bracing FBD is not too high in with respect to the yield force, Fy* of the original structure (i.e. FBD / Fy*< 1.3), and ii) the stiffness of the braced structure is not too high with respect to the original structure (i.e. TB* / T* > 0.2). During the third year the robustness of the technique was verified and a simplified design procedure, based on the linear analysis with q-factor, was proposed as alternative to non-linear methods. Moreover, the non-linear dynamic analysis (NLDA) and non-linear static analysis (NLSA), performed on a benchmark case by using two different finite element programs (CDS-Win and SAP2000), were completed and compared. The benchmark structure was a 4 storey rectangular plan (structure type 2) located in a high seismic zone. A good agreement between numerical results was observed, this demonstrates the effectiveness of commercial software in the simulation of the seismic behavior of buildings with such passive protection systems. The selected case study was selected as example for the application of the proposed design procedure in the Guidelines for the design of passive energy dissipation systems. Regarding to the activities targeted to analysis of problems related to the implementation of the energy dissipation to existing framed buildings, starting from the monotonic moment-curvature analyses performed by varying different parameters (axial load ratio, volumetric transverse reinforcement ratio, longitudinal bars percentage, concrete strength and steel grade) a design equation linking the curvature ductility to transverse reinforcement amount to be provided to RC section has been derived. In the non-linear analyses the BGL model has been used for evaluating the confinement effects on section response. As far as the nonlinear behavior of poorly detailed concrete buildings with smooth bars is concerned, the influence of anchorage loss of passing bars within joint panel has been investigated. The nonlinear analyses have been performed on an internal beam-column joint reproducing a connection of the concrete 3D frame, made up in scale 2:3 and designed only for vertical loads. The numerical investigations, taking also into account slippages effects, have been compared with the experimental results of the joint that has been subjected to two consecutive tests: without and with FRP wraps applied at the columns zones near the panel joint. The last intervention may simulate a local strengthening of columns critical regions when braced system is applied. Starting from this preliminary study, the loss of anchorage of passing bars within the joint panel may also be simulated into the entire model of the 3D


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concrete frame. The obtained nonlinear fiber model will allow us to evaluate the interactions among failure mechanisms observed on the experimental tests of RC subassemblages reproducing beam-column joints of the entire structure. An extensive study on damped SDOF systems has been developed aimed at deriving a relationship between the force reduction factor R and the ductility demand μ, under a specific criterion of equal structural safety level between the damped and the corresponding undamped system. The analyses have been carried out for values of damping ratio between 0.05 and 0.35 and showed that the force reduction factor R is basically not influenced by the damping ratio. Thus, for practical purposes, the force reduction factor for structures with added dampers can be assumed approximately equal to the force reduction factor for systems without added dampers (typically provided by codes). Furthermore, the analyses show that increasing viscous damping significantly decreases the coefficient of variation of R, thus providing a higher level of structural safety (in terms of robustness) with respect to the case of structures without additional viscous. Based on this result, a global reduction coefficient ntot (accounting for both the ductile capacity of the structure and the amount of damping ratio provided by the added dampers) has been proposed to be applied to the elastic spectrum for structures equipped with added viscous dampers. As far as the third objective is concerned, an innovative conceptual design approach is proposed aimed at obtaining an optimized seismic behaviour of the building structure. The approach leads to an “enhanced first-storey seismic isolation system”, which is borrowed from the idea of soft-storey isolation, first proposed in the late ’60 by Fintel and Khan and revised according to the Performance Based Seismic Design framework. Among all the possible solutions, the seismic story isolation can be obtained through the insertion of special hysteretic devices at the bottom level of the building only. These special elements (called “Crescent-Shaped Braces”) are designed in order to satisfy the prefixed multiple seismic performance objectives, also accounting for P-D effects. The performances of the building under multiple earthquake design levels are finally verified through non-linear time-history analyses. 4.3.3. Development of simplified methods for designing dissipative coupling systems among adjacent structures The activity was intended to continue the case studies concerning the structural control and the possibility of integration with monitoring systems. In particular, it has been defined a strategy for the design of dissipation systems in adjacent structures (Figure. 26 a, b, c, d) which is based on the parametric analysis of eigenvalues varying the design parameters (stiffness, h, and viscous element, g, of the device, Figure. 26 e and f). The result of this activity was the creation of a design map for a dissipative element elastic-viscous (rheological model of Kelvin-Voight) and viscous fluid (rheological model of Maxwell), see Figure. 26 g, h. A more detailed description of the modeling, implementation and testing of the strategy is shown in (Antonacci et al., 2012a). Moreover, this method has also been adopted in the activities concerning the seismic retrofitting of structures of the Faculty of Engineering (Antonacci et al., 2012b). Finally, all the work was synthesized in the manual for the design of the devices in the chapter on the dissipative coupling.


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(a) (b)

(c) (d)

(e) (f)

(g) (h)

Figure 26. Adjacent structures: (a) tall parallel buildings, (b), (c) weakly coupled substructures in complex buildings or bridges, (d) synthetic equivalent model to 2gdl composed by 2 simple oscillators coupled

through different models of the device. Loci of the eigenvalues varying γ with η constant, represented in the Argand plane: (e) Kelvin-Voigt model, (f) Maxwell model. Design maps for a dissipative connection of

two simple oscillators: (g) Kelvin-Voigt model, (h) Maxwell model.


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4.3.4. Drafting of the design manual The final purpose within Activity 3 was to write a manual that could be useful to engineers who want to design a new/existing structure with dissipative systems. Dissipative braces and dissipative coupling systems are considered. The manual is organized into two parts. The first part is an introduction whose index follows what was established during the plenary meeting of March 22, 2012, at Piccolo Auditorium Reiss Romoli in Coppito (AQ). The index is the following: - Purpose of the manual; - Protection Strategies; - Current Codes; - Protection Systems; - State of art;

• Rate-independent devices; • Rate-dipendent devices;

- Dissipative braces: configuration and arrangement; - Other types of device.

The second part, instead, lists the design methods. Regarding this, several papers were studied. These were analyzed and summarized in flow-charts and then divided for kind of device and design method. In particular the following devices are considered: - Viscous devices; - Viscoelastic devices; - Hysteretic devices (yield or friction devices).

The identified design methods, instead, can be summarized as follow: - target damping method, where a surplus of damping is established to be assigned to the

structure by dampers; - performance point method, where the bare frame is subjected to push over analysis.

Comparing the behaviour of the structure with the seismic request, the dampers characteristics are designed.

Several study cases are presented.

4.4 ACTIVITY 4: Integration among semi-active control, monitoring and early warning systems

As part of the JETBIS project, investigations have been performed regarding the use of semi-active seismic protection devices integrated with monitoring systems and early warning. The research group has produced advances in research on the possible integrated use of the technologies mentioned above. In particular, concerning the seismic protection system proposed during the first year, consisting in the smart passive use of variable (magnetorheological) dampers based on a prior knowledge of parameters measuring the seismic intensity of upcoming events, provided an early warning system earthquake be present, the research activity was preliminary to: - Measure the robustness of the proposed control system over the uncertainties of the

information (intensity measurements) from the early warning system and related to the upcoming earthquake.

- Investigate the possibility of adopting such a integrated technique of seismic protection for bridges, but also for existing buildings.


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- Investigate the possibility of defining "regional" control algorithms which, again based on prior information provided by the early warning system, are able to lead to the optimal calibration of the devices according to the local seismic hazard and local response expected.

The research also focused on specific aspects related to the mechanical characterization, the response promptness and the dissipative capability of magnetorheological dampers. Further investigations were conducted, in particular, on the numerical modeling of the hysteretic behavior of these devices, the formulation and calibration of models (built in the Simulink) of structures with controlled semi-active techniques. These models are calibrated on the basis of experimental results and can be helpful to: - Assess the functioning and effectiveness of control algorithms from literature. - Investigate possible methods of calibration of these algorithms. - Simulate the effectiveness of semi-active control when driven by information coming from a

seismic early warning system.

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Figure 27. Final results of the comparative analyzes.

An analysis of the experimental data recorded during the campaign JetPacs carried out under the project ReLUIS I has been performed, with the purpose of comparing the effectiveness of the 4 control algorithms adopted for the seismic protection of a 2-storey steel frame equipped with 2 magnetorheological dampers, tested on a shaking table. The preceding figure 27 shows one of the final results of these comparative analyzes: it contains the measure of 6 performance indices Ji (ratio of the maximum values the analysis of the controlled and uncontrolled structure leaded to in terms of: 1. interstorey drift at the first level, 2. interstorey drift at the second level, 3. base shear, 4. control forces, 5. stroke of the devices, 6. sum of elastic and kinetic energies related to the use of each of the four control algorithms under the action of the same earthquake. The research group during the third year produced further advances in research on the possible integrated use of technologies mentioned above. In particular, concerning the seismic protection system proposed and partially analyzed during the first two years, consisting in the smart passive use of variable (magnetorheological, MR) dampers based on prior knowledge of parameters measuring the seismic intensity of upcoming events, provided an early warning system earthquake, the research has been addressed to:


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- assess the robustness of this control system against undesired, even possible, malfunctioning of the control chain (e.g. false alarms, uncorrect prediction of the seismic intensity, electrical black out and related problems of power supplying for the MR devices);

- generate “regional" control algorithms which, again based on prior information provided by the early warning system, are able to lead to the optimal calibration of the devices according to the local seismic hazard and local expected response.

Research has also focused on specific aspects related to the responsiveness of magnetorheological dampers, in particular by carrying out a statistical study of the delays in the response of two devices prototypes subjected to hundreds of tests and arriving, finally, to generate approximate formulas for the time delay prediction. Still aimed at integrating technologies of a different nature, an experimental campaign was conducted by shaking table tests (at the laboratory of the RU of Naples Federico II) of a steel frame that, equipped with recycled rubber isolators, was "controlled" at the base with semi-active devices. These hybrid control tests were intended to show how the use of semi-active devices coupled to the base isolators can be useful to correct the modal shapes, in particular to the attainment of a first mode as tending to the rigid motion of the superstructure.

Figure 28. Experimental tests on shaking table.

5 DISCUSSION

The activities carried are fully in line with the timesheet reported in the initial proposal of Line 2.3 of Task 3 within RELUIS project. The planned objectives have been achieved and the results are satisfactory even though a further development on a larger sample of real structures is needed. The subdivision of the research project into activities and their subdivision in arguments and phases allows to check the development and the fulfillment of the proposed intermediate goals. In the third year connection with other research units from this task and task AT3.1.3 have been reinforced, in particular relating to the JETBIS project (Joint Experimental Testing on Base Isolation Systems). Links have been established among UNINA, POLIBA, UNIBAS, POLIMI, UNIPARTH, UNICAL and UNIUD for the development of JETBIS project. The activity on the Observatory on isolated structures in L'Aquila has been conducted by means a cooperation between UNINA_DL and UNIVAQ.


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6 VISIONS AND DEVELOPMENTS

The following activities have been planned on the seismic isolation: 1) Technical Reports tests first project JETBIS and reports summarizing the results of

numerical simulations and comparison with experimental data. Taking up any new experimental activities supplementary to investigate the effects of bi-directional behavior of the devices under investigation and subsequent elaboration and updating of codes.

2) Technical report on the use of seismic isolation for the retrofitting of existing structures considering the hike in the plastic range of the superstructure.

3) Technical Reports of tests on seismic isolation devices based on innovative materials. Definition / upgrade of test protocols for the qualification / acceptance.

4) Design provisions and regulations for the control of unwanted movements of isolation systems due to residual displacements, differential motions and vertical displacements.

5) Technical Reports of experimental evidence relating to the applicability of seismic isolation precast structures.

6) Definition of design methods, procedures and software dedicated seismic isolation and proposed regulations developed under this project.

On the other hand, for the dissipation topic the following activities have been scheduled:

1) Guidelines with design methods for structures with energy dissipation systems based on: dissipative braces, coupled with seismic isolation systems and coupling of adjacent medium / high. Guidelines / additions regulations.

2) Technical Reports of tests on energy dissipation devices based on new materials and technologies. Definition / upgrade of test protocols for the qualification / acceptance.

3) Technical Reports of tests for systems of dissipation mechanisms associated with rocking for the seismic protection of prefabricated structures.

4) Review and update of the reference standards in relation to the definition of the properties of the system power dissipation, modeling and structural analysis and test procedures for the qualification / acceptance.

5) Definition of algorithms for integrated control systems, obtained by the combined use of semi-active devices for seismic early warning systems.

6) Definition of design methods, procedures, systems and software designed for energy dissipation and regulatory proposals developed under this project.

7 MAIN REFERENCES

Antonacci E., De Stefano A., Gattulli V., Lepidi M. and Matta E. (2012a). “Comparative study of vibrationbased parametric identification techniques for a three-dimensional frame structure”. Journal of Structural Control and Health Monitoring, n. 19 (5), pp. 579-608.

Antonacci E., Gattulli V., Martinelli A., Vestroni F (2012b). “La Basilica di S. Maria di Collemaggio in L'Aquila: prima e dopo il terremoto”. In L. Milano, C. Morisi, C. Calderini, A. Donatelli (Editors), "L'Università e la Ricerca per l'Abruzzo: il patrimonio culturale dopo il terremoto del 06 Aprile 2009", Textus Edizioni, pp. 45-51. ISBN 978-88-87132-80-9.

Antonacci E., Gattulli V., Galeota D., Fanale L. (2012c). “Analisi del danno strutturale e del comportamento sismico di Palazzo Carli”. In L. Milano, C. Morisi, C. Calderini, A. Donatelli (Editors), "L'Università e la Ricerca per l'Abruzzo: il patrimonio culturale dopo il terremoto del 06 Aprile 2009", Textus Edizioni, pp. 92-97. ISBN 978-88-87132-80-9.


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Braga F., Gigliotti R., Laterza M., D’Amato M., Rajbhandari S.N. (2013).”Modeling of longitudinal passing bars within the joint panel in poor anchorage condition”. XV Convegno Anidis “L’ingegneria Sismica In Italia”, Padova (Italy).

Braga F., Gigliotti R., Laterza M., D’Amato M., Kunnath S. (2012).”A modified steel bar model incorporating bond-slip for seismic assessment of concrete structures. ASCE, Journal of Structural Engineering , 138(11): 1342-1350.

Cardone D., Flora A., Gesualdi G. (2012). “Inelastic response of RC frame buildings with seismic isolation. Earthquake Engng. Struct. Dyn. DOI: 10.1002/eqe.2250.

Castaldo P., De Iuliis M. (2013). “Optimal integrated design of structural and viscoelastic bracing-damper systems: theoretical principles”. XV Convegno ANIDIS 2013: L’Ingegneria Sismica in Italia, Padova (Italia). Padova University Press, ISBN: 9788897385592, pp. 1-10.

Kim, Y. S. & Yun, C. B. (2007). “Seismic response characteristics of bridge using double concave friction pendulum bearings with tri-linear behavior”. Engineering Structures, Vol 29(11): 3082-3093.

UNI EN 15129:2009. Antiseimic Devices.

8 RELUIS REFERENCES

Cardone D., Flora A., Gesualdi G. (2012). “Inelastic response of RC frame buildings with seismic isolation”. Earthquake Engng. Struct. Dyn. DOI: 10.1002/eqe.2250.

Cardone D., Flora A., Gesualdi G. (2012).“Inelastic behavior of base-isolated RC frame buildings”. Proc of. 15WCEE, Lisboa (Portugal).

Caterino N., Spizzuoco M., Occhiuzzi A. (2013). “Promptness and dissipative capacity of MR dampers: experimental investigations”. Structural Control and Health Monitoring. DOI: 10.1002/stc.1578.

Caterino N., Spizzuoco M. (2013). “Response time of MR dampers for seismic semiactive control: experimental measures and possible prediction”. COMPDYN 2013, 4th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, M. Papadrakakis, V. Papadopoulos, V. Plevris (eds.), Kos Island (Greece).

Caterino N., Spizzuoco M., Occhiuzzi A. (2013).“Shaking table tests to compare semi-active control algorithms for variable dampers”. COMPDYN 2013, 4th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, M. Papadrakakis, V. Papadopoulos, V. Plevris (eds.), Kos Island (Greece).

Comodini F., Mezzi M. (2013). "Analisi comparative per l’ottimizzazione di dispositivi di protezione sismica a basso costo per strutture prefabbricate" ANIDIS 2013 XV Convegno L'Ingegneria Sismica in Italia. Padova, Italia. ISBN 9788897385592

Diaferio M., Foti D., Nobile R. (2010). “The Dynamic Experimental Behaviour of a New Aluminium Passive Protection Device in a 3D Frame”, Atti della “14 European Conference on Earthquake Engineering”, 30 August-3 September 2010, Ohrid, Macedonia.

Diaferio M, Foti D, Vacca S (2013). “Preliminary analysis and characterization of a base isolater made with steel cylinders rolling on rubber layers”. In: Workshop on “Dynamics, stability and control of flexible structure” - Book of Abstracts. Senigallia, Italy.

Di Cesare A., Ponzo F.C., Nigro D. (2013). “Assessment of the Robustness of Hysteretic Energy Dissipating Bracing Systems”. Bull Earthquake Eng BEEE-S-13-00128 (submitted).

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